FROM THE PREFACE: Dramatic adjustments ensue within the body structure of such a lot animals in the course of their improvement. one of the vertebrates, birds are fullyyt oviparous, reside for variable classes in a cleidoic egg, and express basic adjustments in excretion, nutrients, and respiratory on the time of hatching. by contrast, the eutherian mammals are all viviparous, rely on the maternal circulate and a really expert placenta to supply nutrients, trade gases, and discharge wastes.